1. Field of the Invention
The present invention relates to a cutter having a plurality of indexable cutter inserts attached to a tool body, and a method for manufacturing the same.
2. Prior Art
In the field of cutting tools, insert cutters, each of which comprises a plurality of indexable cutter inserts of a hard material such as cemented carbide releasably attached to a tool body of a steel such as tool steel, are extensively used.
In the cutters of this type, in order to prevent the outer peripheral surface of the tool body from being damaged due to the abrasion caused by cutting chips to thereby improve the durability of the tool body, the hardness of the tool body at its surface is enhanced to about H.sub.R C 45 by subjecting the tool body to quench hardening.
However, when the tool body is subjected to quench hardening, the tool body inevitably undergoes quenching distortion. For this reason, after the quench hardening, recesses for receiving inserts or those portions to be secured to a machine tool, such as the surface of a boss of a tool body in a face milling cutter or the outer surface of the shank in an end mill, which are all required to be formed with high precision, must be subjected to sanding or to cutting work using an end mill in order to remove the distortion. Therefore, an increase in cost due to the greater amount of labor required cannot be avoided. In addition, the removal of distortion is prolonged when the quenching distortion is large, and the cost of working is thereby further increased.
Furthermore, when carrying out the cutting work after the quench hardening, the cutting edge of the end mill used for the cutting work undergoes wear since the hardness of the tool body at the surface has been enhanced to no less than H.sub.R C 45, and in addition, the cutting accuracy is adversely affected. In particular, when working a plurality of insert-receiving recesses successively, the working precision is largely varied between the recess formed immediately after the commencement of the working and the recess formed at the end of the working. As a result, the run-outs of the inserts secured to the insert-receiving recesses are increased, so that the cutting accuracy is unduly deteriorated.
Furthermore, a great residual stress often occurs in the interior of the tool body due to the quenching during the hardening treatment, and the precision is lowered when such stress is later released.